This invention relates to a device for controlling engine torque in a vehicle, and more particularly to a device for controlling engine torque in a vehicle mounted thereon with an automatic transmission, wherein satisfactory shift characteristics can be obtained in association with environmental conditions while the engine is running.
Previously, automatic transmissions have been constructed such that a gear mechanism and a plurality of frictionally engaging devices are provided, and a hydraulic control system is operated to selectively change the engagement of the frictionally engaging devices, to thereby achieve any one of a plurality of gear stages.
There have been also proposed many methods of integrally controlling the automatic transmission and the engine, wherein engine torque is changed during shifting (e.g. Japanese Patent application Laid-Open (Kokai) No. 69738/1980). When the amount of torque transmitted from the engine is changed during shifting, the amount of absorbed energy in members of the automatic transmission or in the frictionally engaging devices for controlling these members can be decreased, so that the shifting is completed with a small shift shock for a short period of time. As a result, a satisfactory shift feeling can be given to a driver, and the frictionally engaging devices can be improved in durability.
Heretofore, when engine torque is changed during shifting, the amount of change is defined in association with the type of shifting and engine load (throttle opening, etc.). However, there is a problem which cannot be satisfactorily solved by this. In particular, even with a constant throttle opening, variations in engine intake air pressure (atmospheric pressure or boost pressure) result in considerable engine output fluctuations. Consequently, where the amount of change in engine torque for a certain shifting is determined only in association with throttle opening, the engine torque after the change fluctuates, thus likewise resulting in fluctuations in the shift characteristics.
In general, the lower the cooling water temperature and the oil temperature, the less the occurrence of engine knocking. Therefore, when the cooling water temperature and the oil temperature are low, control is often performed to advance ignition timing. In this case, even with the same throttle opening, the engine torque is rather high.
On the other hand, even when a constant engine output is used, i.e. the engine torque after the change is the same as before, the optimal turning point of frictionally engaging devices is different depending upon whether the oil temperature in the frictionally engaging devices in the automatic transmission is high or low. In general, when the oil temperature is very low, the visocity of the oil is high, so that the responsiveness of the frictionally engaging devices becomes rather slow. Furthermore, when the oil temperature becomes high, the amount of oil leakage in oil lines increases, whereby the responsiveness of the frictionally engaging devices also becomes rather slow. This means that, as viewed from the side of the automatic transmission, such an adverse influence is brought about when the engine output is shifted to the higher side.